Optical sensor, and devices incorporating the same

ABSTRACT

An optical sensor including an abutment part configured to abut one edge of an object to be measured, a wall extending along a side of the object to be measured and having a first opening to pass light emitted to the object to be measured, and a first concave portion formed between the first opening and the abutment part on a side of the wall to position the object to be measured. A paper-type discrimination device including the optical sensor, and a controller configured to discriminate a paper type of the object using the reflection light from the object measured by the optical sensor. An image forming apparatus including the optical sensor or the paper-type discrimination device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. §119(a) to Japanese Patent Application Nos. 2014-240041 and2014-241561, filed on Nov. 27, 2014, and Nov. 28, 2014, respectively, inthe Japan Patent Office, the entire disclosure of which is herebyincorporated by reference herein.

BACKGROUND

1. Technical Field

Embodiments of the present invention relate to an optical sensor, apaper-type discrimination device having the optical sensor, and an imageforming apparatus having the paper-type discrimination device.

2. Background Art

As an optical sensor that irradiates an object to be measured withlight, for example, the technology to discriminate the type of paper bymeasuring the bumps and dips of the surface of the paper, which isprovided for image forming apparatuses such as a copier, facsimile(FAX), and a printer, is known in the art. As such a technology used forpaper-type discrimination, optical sensors that irradiate paper withlight and use the reflection light from the paper to discriminate thetype of the paper are known.

In order to discriminate the types of paper with high accuracy using anoptical sensor, it is desired that the irradiating point of light befixed regardless of the type of the paper. For this reason, aconfiguration is known in the art in which an opening is formed on aplane having a certain angle with reference to the incidence directionof the light and the light reflected from the portion of the planeexposed by the opening is measured.

SUMMARY

Embodiments of the present invention described herein provide an opticalsensor including an abutment part configured to abut one edge of anobject to be measured, a wall extending along a side of the object to bemeasured and having a first opening to pass light emitted to the objectto be measured, and a first concave portion formed between the firstopening and the abutment part on a side of the wall to position theobject to be measured.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of exemplary embodiments and the manyattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings.

FIG. 1 is a diagram illustrating a schematic configuration of an imageforming apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a diagram illustrating a schematic configuration of apaper-type discrimination device according to the first embodiment ofthe present invention.

FIG. 3 is a diagram illustrating a schematic configuration of an opticalsensor according to the first embodiment of the present invention.

FIG. 4A and FIG. 4B are schematic diagrams illustrating a feature of thefirst embodiment of the present invention.

FIG. 5 is a schematic diagram of an example of the reflection lightmeasurement of the optical sensor illustrated in FIG. 3.

FIG. 6A, FIG. 6B, and FIG. 6C are diagrams illustrating examples of thereflection light that is measured by the reflection light measurementillustrated in FIG. 5.

FIG. 7 is a diagram illustrating an example of paper informationaccording to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating an example configuration of an opticalsensor according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating an example configuration of an opticalsensor according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating an example configuration of an opticalsensor according to a fourth embodiment of the present invention.

FIG. 11 is a block diagram depicting example processes performed by theoptical sensor illustrated in FIG. 10.

FIG. 12 is a diagram illustrating an example configuration of an opticalsensor according to a fifth embodiment of the present invention.

FIG. 13 is a diagram illustrating an example of the intensitydistribution of the transmission light measured by thetransmission-light detector illustrated in FIG. 12.

The accompanying drawings are intended to depict exemplary embodimentsof the present disclosure and should not be interpreted to limit thescope thereof. The accompanying drawings are not to be considered asdrawn to scale unless explicitly noted.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“includes” and/or “including”, when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In describing example embodiments shown in the drawings, specificterminology is employed for the sake of clarity. However, the presentdisclosure is not intended to be limited to the specific terminology soselected and it is to be understood that each specific element includesall technical equivalents that have the same structure, operate in asimilar manner, and achieve a similar result.

In the following description, an embodiment of the present invention isdescribed with reference to the drawings. FIG. 1 illustrates an outlineof the configuration of an image forming apparatus 200 that serves as anoptical sensor according to an embodiment of the present invention.

As illustrated in FIG. 1, the image forming apparatus 200 form an imagebased on the image data obtained from an externally-provided host device400, for example, a personal computer (PC). The image forming apparatus200 includes an image forming unit 23 that forms an image on a transferbelt 240 that serves as an intermediate transferor, and a sheet feeder26 that feeds paper P to the image forming unit 23. The image formingapparatus 200 includes a transfer roller 242 that transfers the imageformed on the transfer belt 240 to the paper P, i.e., an object to bemeasured, at a secondary transfer position N, and a fixing device 25that uses heat and pressure to fix the image transferred at thesecondary transfer position N onto the paper P. The image formingapparatus 200 includes a registration roller pair 256 that conveys thepaper P fed into the sheet feeder 26 to the secondary transfer positionN at a prescribed timing, and an output roller pair 258 that outputs thepaper P on which the image has been fixed by the fixing device 25 to apaper output tray 270. The image forming apparatus 200 includes acommunication controller 280 that controls bidirectional communicationwith the host device 400 through the network or the like, and a printercontroller 290 that serves as an image-processing controller to controlthe mechanism related to the image formation performed by the imageforming apparatus 200. Further, the image forming apparatus 200 isprovided with an optical sensor 100 near the operation panel, in such amanner that an operator can operate the optical sensor 100. The opticalsensor 100 irradiates the paper P with light and measures the lightreflected from the paper P to discriminate the type of the paper P andobtain paper information Q.

In the present embodiment, cases in which the image forming apparatus200 is provided with the optical sensor 100 are described. However, theoptical sensor 100 may independently be provided. The type of the paperP described herein indicates types including, for example, plain paper,coated paper such as gloss-coated paper, and special paper such asembossed paper. Moreover, the type of the paper P described hereinindicates, for example, the quality of paper, the presence of surfacetreatment such as coating, and the brand of the paper. It is desiredthat the object to be measured be sheet-shaped or thin-plate-shaped soas to be insertable from a slot 111. Alternatively, the object to bemeasured may be, for example, a cloth, cutting sheet, or a substrate,other than the paper P that serves as a recording medium. In such cases,the type of the object to be measured includes, for example, a materialsuch as vinyl, cloth, and plastic, presence of surface treatment, thebrand, and the surface condition.

The image forming unit 23 is accommodated in the image forming apparatus200 to serve as a unit of four image forming stations that correspond tothe basic colors of cyan, magenta, yellow, and black, respectively. Forthe purpose of simplification, only one of the four image formingstations of the image forming unit 23 is described, and the descriptionof the other similarly-configured three image forming stations isomitted. The image forming unit 23 includes a drum-shaped photoconductor230 that serves as a latent-image bearer, an optical scanner 210 thatserves as an exposure device and optically-writing unit to form a latentimage on the photoconductor 230, and a developing device 233 that formsa toner image on the photoconductor 230 on which the latent image hasbeen formed. The image forming unit 23 includes a cleaning device 231that removes the toner from the photoconductor 230 after the toner imageformed on the photoconductor 230 has been transferred to the transferbelt 240, and a charging device 232 that electrically charges thephotoconductor 230 from which the toner has been removed. Thephotoconductor 230, the charging device 232, the cleaning device 231,and the developing device 233 are used as a unit and together configurean image forming station.

The photoconductor 230 is a drum-shaped rotor on which a photosensitivelayer is formed, and the photosensitive layer is a surface to be scannedby the scanning light of the optical scanner 210. The photoconductor 230is driven by a driver in A-direction as illustrated in FIG. 1.

The charging device 232 is a charger disposed on a downstream side ofthe cleaning device 231, on an upstream side of the optical scanner 210in the A-direction. The charging device 232 evenly charges the surfaceof the photoconductor 230. The charging device 232 may perform chargingby corona discharge, or may use a charging brush or a charging roller toperform charging.

The optical scanner 210 scans each of the surfaces of theelectrically-charged photoconductor 230, with the scanning light that ismodulated for each color based on the multicolor image data receivedfrom the printer controller 290. By so doing, an electrostatic latentimage that is drawn by electrical potential is formed on the surface ofthe photoconductor 230.

The developing device 233 thinly and evenly applies the toner of thecorresponding color onto the surface of a development roller 233 a byrotating the development roller 233 a. When the toner that has beenapplied to the surface of the development roller 233 a is brought intocontact with the surface of the photoconductor 230 of the correspondingcolor, the toner moves and adheres only to the portions of the surfaceof the photoconductor 230 that are irradiated with the scanning light,i.e., the portions exposed by the scanning light. In other words, thedeveloping device 233 renders the latent image manifest by making thetoner adhere to the latent image formed on the photoconductor 230, toform a toner image on the photoconductor 230.

The toner images that are formed on the photoconductors 230 aresequentially transferred to the transfer belt 240 at specified timingaccording to transfer bias. Then, the transferred toner images of thefour basic colors are superimposed on top of one another to form amulticolor image.

A sheet feeder 26 includes a sheet tray that accommodates the paper P,and a plurality of feeding rollers 254 that convey the paper Paccommodated in the sheet tray towards the registration roller pair 256.

The fixing device 25 includes a heating roller 251 having a heat sourceinside, and a pressure roller 250 that forms a fixing nip together withthe heating roller 251. The paper P bearing a toner image runs throughthe fixing nip of the fixing device 25, and the toner image is fixed byheat and pressure on the surface of the paper T. The heating roller 251includes a cylinder roller made of aluminum, a silicone rubber layerformed around the peripheral surface of the cylinder, and a halogenheater disposed inside the cylinder.

The printer controller 290 includes, for example, a central processingunit (CPU), a read-only memory (ROM) in which a program described byCPU-readable codes and various kinds of data used for executing theprogram are stored, and a random access memory (RAM) that serves as aworking memory. In the printer controller 290, a plurality of types ofthe paper P that can be used for the image forming apparatus 200 arestored. Moreover, in the printer controller 290, the image-formingconditions that are optimal for each of the types of the paper P, i.e.,image-processing conditions such as development conditions, exposureconditions, and transfer conditions, are stored as a development andtransfer table 291 (see FIG. 7).

Note that the development conditions include, for example, the tonerconcentration at the developing device 233, and developing bias. Theexposure conditions include, for example, the intensity of the laserbeam emitted from the optical scanner 210 to the photoconductor 230,i.e., the latent-image writing intensity. The latent-image writingintensity is equivalent to the scanning light intensity. The transferconditions include, for example, a primary transfer bias, i.e., thepotential difference with which the toner image is transferred from thephotoconductor 230 to the transfer belt 240, or a primary transfercurrent value, i.e., the current value with which the toner image istransferred from the photoconductor 230 to the transfer belt 240.Moreover, the transfer conditions include, for example, a secondarytransfer bias, i.e., the potential difference with which the image istransferred from the transfer belt 240 to the paper P, or a secondarytransfer current value, i.e., the current value with which the image istransferred from the transfer belt 240 to the paper P.

FIG. 2 is a diagram illustrating an example of a schematic configurationof a paper-type discrimination device according to the presentembodiment. As illustrated in FIG. 2, the optical sensor 100 isconnected to the printer controller 290 through a cable 2201, and theoptical sensor 100 sends the paper information Q to the printercontroller 290 through the cable 2201. Moreover, the optical sensor 100includes a housing 101, and a slot 111 into which the paper P isinserted in the X direction. The X direction may be referred to as aninsertion direction.

FIG. 3 is a diagram illustrating an example configuration of the opticalsensor 100 according to the present embodiment. As illustrated in FIG.3, the optical sensor 100 is arranged on the other side of the slot 111.In other words, the optical sensor 100 is arranged at an end in the Xdirection. Moreover, the optical sensor 100 includes an abutment part130 that contacts one edge of the paper P to perform positioning for thepaper P, and a wall 131 that abuts one of the surfaces of the paper P.Moreover, the optical sensor 100 includes a first aperture 110 that isformed on the wall 131 to irradiate an irradiation center O, which isany desired part on the paper P, with light, and a first concave portion121 that has a concave shape in the normal direction of the Z-axis andis formed between the first aperture 110 and the abutment part 130 onthe wall 131 side.

Moreover, the optical sensor 100 includes a light source 11 that isdisposed in the normal direction of the Z-axis with reference to thewall 131 inside the housing 101, and a collimator lens 12 thatcollimates the light emitted from the light source 11. Moreover, theoptical sensor 100 includes a detector 133 having three photodetectorsthat measure the reflection light from the paper P. Moreover, theoptical sensor 100 includes a supporting member 103 that presses thepaper P against the wall 131 or the periphery of the first aperture 110from the other side of the wall 131. Note that the supporting member 103serves as a pressurizer in the present embodiment. Further, the opticalsensor 100 includes a controller 105 that controls the signals of theelements of the optical sensor 100.

The housing 101 is a box made of aluminum, and the surface of thehousing 101 is anodized in black in order to reduce the influence ofdisturbance light and stray light. The slot 111 is formed to have acontinuous opening to three planes including the front plane of theoptical sensor 100 in the reverse direction of the X-axis of the housing101, the side planes orthogonal to the Y-axis.

The cable 2201 is a route of power supply that connects the printercontroller 290 to the optical sensor 100. The cable 2201 may be, forexample, a universal serial bus (USB) cable or an RS-232C. Moreover, thecable 2201 is a transmission route through which the paper information Qsuch as the reflectance measured by the optical sensor 100 istransmitted to the printer controller 290.

The abutment part 130 is a part of the housing 101 that is a planeorthogonal to the X-axis, and is arranged at the end of the slot 111 inthe X direction. The wall 131 abuts the surface of the paper P in astate where one edge of the paper P in the normal direction of theX-axis contacts the abutment part 130, and supports the paper P withsupporting member 103 parallel to the XY plane. Moreover, the wall 131has the first aperture 110 that is circularly formed around the point ofthe irradiation center O at which the light emitted from the lightsource 11 is emitted. It is desired that the first aperture 110 bedisposed near the center of the paper P that is in a state of contact.

FIG. 4A and FIG. 4B are schematic diagrams illustrating a feature of thefirst embodiment of the present invention. The first concave portion 121is a recess formed at a portion between the first aperture 110 and theabutment part 130, and may be a notch or hole, or a trench. Asillustrated in FIG. 4A and FIG. 4B, the first concave portion 121 isarranged such that the edge of the paper P in the normal direction ofthe X-axis, in a state of contact, can enter the inside of the firstconcave portion 121.

The supporting member 103 includes a pressing plane 103 a that isarranged opposed to the wall 131 to press the paper P against the wall131, a leg part that supports the pressing plane 103 a, and a spring 104that is provided for the leg part to serve as a pressing member.Moreover, the supporting member 103 includes a paper-thickness sensor120 that measures the displacement caused on the pressing plane 103 a inthe Z-axis direction. At the edge of the supporting member 103 on theupstream side of the insertion direction (i.e., at the edge of thesupporting member 103 in the reverse direction of the X-axis), aninclined portion 103 b that is inclined with reference to the pressingplane 103 a is formed to make the insertion of the paper P easier. In aninitial state where the paper P has not yet been inserted, thesupporting member 103 is pressed against the wall 131 in the normaldirection of the Z axis due to the force exerted by spring 104. In otherwords, the supporting member 103 is maintained in a state where thepressing plane 103 a contacts the wall 131.

The paper-thickness sensor 120 is a displacement converter in acantilevered state, and is attached to the supporting member 103. Thepaper-thickness sensor 120 measures the displacement of the supportingmember 103 when the supporting member 103 moves down due to theinsertion of the paper P. In other words, the paper-thickness sensor 120measures the displacement caused on the pressing plane 103 a in theZ-axis direction, with reference to the position of the pressing plane103 a that abuts the wall 131 in the initial state. More specifically,the paper-thickness sensor 120 outputs to the controller 105 pulsesignals whose number of the signals is proportional to the amount ofdisplacement of the cantilever, and the controller 105 counts the numberof the pulse signals. Accordingly, the amount of the displacement of thecantilever is calculated. In the present embodiment, the paper-thicknesssensor 120 is a displacement converter in a cantilevered state. However,the paper-thickness sensor 120 may be a noncontact displacement gageusing laser, or a differential-transformer displacement gage.

The light source 11 is a semiconductor laser beam source having avertical-cavity surface-emitting laser (VCSEL) array where a pluralityof VCSEL elements are two-dimensionally arranged. The light emitted fromthe light source 11 is collimated by the collimator lens 12, and thecollimated laser-beam bundle is emitted to the irradiation center O. Asdescribed above, the first aperture 110 is arranged around theirradiation center O formed on the wall 131. Accordingly, when the paperP is in a state of contact, the light passes through the first aperture110 and is emitted to the paper P.

Assuming that the light is incident on the boundary surface of a medium,i.e., the boundary surface between the paper P and the air in thepresent embodiment, the plane that includes the incident light beam andthe normal line drawn from the point of incidence of the boundarysurface is referred to as an incidence plane. As the light source 11includes a plurality of two-dimensionally arranged laser-light emittingelements, there are a plurality of incidence planes whose number isequal to the number of the laser-light emitting elements. However, forthe sake of explanatory convenience, the incidence plane of the lightthat enters the irradiation center O is referred to as the incidenceplane of light source 11 on the paper P. In other words, the plane thatincludes the irradiation center O and is parallel with the XZ-plane isthe incidence plane in the present embodiment.

The light that is polarized in the direction perpendicular to theincidence plane is referred to as an S-polarized light, and the lightthat is polarized in the direction perpendicular to the S-polarizedlight is referred to as a P-polarized light. In other words, the lightwhere the oscillating direction is perpendicular to the XZ plane is theS-polarized light, and the light where the oscillating direction isparallel to the XZ plane is the P-polarized light. In the followingdescription, for the purpose of simplification, the terms “S-polarizedlight” and “P-polarized light” are also used for the reflection light aslong as the polarization direction of the reflection light is equivalentto the polarization direction of the light that enters the paper P.

FIG. 5 is a schematic diagram of an example of a reflection lightmeasurement of the optical sensor 100 illustrated in FIG. 3, accordingto the present embodiment. The light emitted from the light source 11 isa linearly polarized light, and irradiates the surface of the paper Pwith the S-polarized light having the first polarization direction. Notethat the angle which the straight line connecting between the lightsource 11 and the irradiation center O forms with the Z-axis in FIG. 5,i.e., the incidence angle θ₀ from the light source 11 is 80 degree.

The detector 133 includes a first photodetector 15 arranged on anoptical path of the light that is emitted from the light source 11 andthen is reflected at the irradiation center O by specular reflection, apolarizing filter 14 that is arranged above the irradiation center O inthe Z-axis direction, and a second photodetector 13 that is arrangedabove the polarizing filter 14 along the extension drawn from theirradiation center O to the polarizing filter 14. Moreover, the detector133 includes a third photodetector 17 that is arranged at a positiondifferent from that of the first photodetector 15 in the normaldirection of the X-axis with reference to the irradiation center O. Eachof the first photodetector 15, the second photodetector 13, and thethird photodetector 17 may be, for example, a photodiode.

The controller 105 includes, for example, an analog-to-digital (A/D)converter that A/D converts the output from the first photodetector 15,the second photodetector 13, and the third photodetector 17, amicrocontroller that controls the operation of the sensor system, amemory, and a logical circuit.

As illustrated in FIG. 5, the first photodetector 15 is arranged suchthat the angle φ₁ which the surface of the paper P forms with a line L2connecting the irradiation center O to the first photodetector 15 is 170degrees.

The polarizing filter 14 is a deflector that transmits the P-polarizedlight and blocks the S-polarized light. Alternatively, the polarizingfilter 14 may be a polarization beam splitter that selectively transmitsthe P-polarized light and the S-polarized light in a similar manner to adeflector. The second photodetector 13 is arranged along the extensiondrawn from the irradiation center O to center of the polarizing filter14, in the normal direction of the Z axis. As illustrated in FIG. 5, theangle φ₂ which the surface of the paper P forms with the line L2connecting through the irradiation center O, the polarizing filter 14,and the center of the second photodetector 13, is 90 degrees.

The third photodetector 17 is arranged such that the angle φ₃ which thesurface of the paper P forms with a line L3 connecting the irradiationcenter O to the center of the third photodetector 17 is 120 degrees.

It is desired that the irradiation center, the center of the lightsource 11, the center of the first photodetector 15, the center of thesecond photodetector 13, and the center of the third photodetector 17 bedisposed on substantially the same XZ plane, and approximately bedisposed on the incidence plane.

The light that is emitted from the light source 11 and enters the paperP may be classified into two kinds of reflected light, consisting of thelight reflected at the surface of the paper P, and the light that entersthe inside of the paper P and then is reflected inside the paper P.Further, the light reflected at the surface of the recording paper maybe classified into two kinds of reflected light, consisting of the lightof regular reflection and the light of diffuse reflection. Regarding thelight that is reflected inside the paper P, multiple scattering occursin the fibers inside the paper P. Accordingly, it is considered thatonly the diffuse-reflected light is detectable.

FIG. 6A, FIG. 6B, and FIG. 6C are diagrams illustrating examples of thereflection light that is measured by the reflection light measurementillustrated in FIG. 5, according to the present embodiment. Thereflection light of the light that is emitted from the light source 11and then enters the paper P is schematically classified into three kindsof reflection light, as illustrated in FIG. 6A, FIG. 6B, and FIG. 6C.FIG. 6A illustrates a surface specular reflection light R1 that isreflected by specular reflection on the surface of the paper P. FIG. 6Billustrates a surface diffuse reflection light R2 that is reflected bydiffuse reflection on the surface of the paper P. FIG. 6C illustrates aninternal diffusion reflection light R3 that is reflected by diffusereflection inside the paper P.

Here, relation between types of the paper P and the above-describedreflection lights are described. Firstly, when the paper P has smoothpaper quality on its surface and almost no penetration into the paper Poccurs, it is assumed that almost all the incident light is reflected onthe surface by specular reflection and almost all the reflection lightis detected as the surface specular reflection light R1.

Secondly, when the surface of the paper P has some bumps and dips, it isschematically considered that planar portions and uneven portions aredistributed over the surface of the paper P at a constant rate accordingto the type of the paper P. In such cases, the light reflected at theplanar portions are detected as the surface specular reflection lightR1, and the light reflected at the uneven portions are detected as thesurface diffuse reflection light R2. Assuming that the planar portionsand the uneven portions appear at random, the surface diffuse reflectionlight R2 is theoretically isotropic on the XZ plane.

The internal diffusion reflection light R3 is a light that enters theinside of the paper P and then returns to the incidence plane asreflected. Accordingly, it is considered that the intensity of theinternal diffusion reflection light R3 varies according to the densityor thickness of the paper P. Moreover, it is considered that theinternal diffusion reflection light R3 is isotropic because the internaldiffusion reflection light R3 can be reflected in any direction in theXYZ space.

Note that in order for the light reflected at the surface of the paper Pto have components other than the S-polarized light, i.e., in order forthe polarization direction to rotate on the surface of the paper P, theincident light needs to be reflected at a portion of the surface that isinclined in the direction perpendicular to the incidence plane. However,the irradiation center, the center of the light source 11, the center ofthe first photodetector 15, the center of the second photodetector 13,and the center of the third photodetector 17 are disposed onsubstantially the same XZ plane. Accordingly, the light that isreflected at a portion of the surface that is inclined in the directionperpendicular to the incidence plane is not detected by the detector133. Accordingly, both the surface specular reflection light R1 and thesurface diffuse reflection light R2 are on the incidence plane. For thisreason, it is considered that the polarization direction of the surfacespecular reflection light R1 and the surface diffuse reflection light R2are substantially the same as that of the incident light and theS-polarized light.

On the other hand, the polarization direction of the internal diffusionreflection light R3 rotates while passing through fibers and goingthrough multiplex polarization. The internal diffusion reflection lightR3 may include the P-polarized components. In other words, only theinternal diffusion reflection light R3 includes the P-polarized light onthe XZ plane when it is assumed that the light source 11 only emits theS-polarized linear light. For this reason, the polarizing filter 14 isarranged between the second photodetector 13 and the irradiation centerO to block the S-polarized light and transmit only the P-polarizedlight. In other words, the polarization direction of the light emittedfrom the light source 11 is offset from the light transmitted by thepolarizing filter 14 by 90 degrees. Accordingly, the secondphotodetector 13 detects only the P-polarized components included in theinternal diffusion reflection light R3. According to the experiments runby the inventor and his associates, it is known that the amount of theP-polarized components included in the internal diffusion reflectionlight R3 is dependent on the length of the path in the fibers of thepaper P through which the light passes and thus correlates with thethickness or density of the paper P.

As the incidence angle θ₀ has 80 degrees, the reflection angle θ_(R1) ofthe surface specular reflection light R1 also has 80 degrees.Accordingly, almost all the surface specular reflection light R1, andsome of the surface diffuse reflection light R2 and the internaldiffusion reflection light R3 enter the first photodetector 15. In otherwords, the first photodetector 15 mainly receives the surface specularreflection light R1. Note that the surface diffuse reflection light R2isotropically disperses on the XZ plane. Accordingly, it is consideredthat the amount of the surface diffuse reflection light R2 received bythe first photodetector 15 is approximately equal to the amount of thesurface diffuse reflection light R2 received by the third photodetector17. On the other hand, the third photodetector 17 barely receives thesurface specular reflection light R1. For this reason, the surfacespecular reflection light R1 and the surface diffuse reflection light R2can separately be measured by calculating the difference between theoutput signal level of the first photodetector 15 and the output signallevel of the third photodetector 17.

As described above, the optical sensor 100 according to the presentembodiment includes the detector 133 that uses the first photodetector15, the second photodetector 13, and the third photodetector 17 tomeasure the reflection light from the paper P.

The optical sensor 100 controls the switching on and off of the lightsource 11 to irradiate the paper P with light according to theinstruction given from the printer controller 290 through the cable 2201or the instruction given from the host device 400, and measures theoutput of each of the photodetectors of the detector 133. Moreover, theoptical sensor 100 sends the measured signal values S′₁, S′₂, and S′₃,which are the results of the measurement performed by each of thephotodetectors, to the printer controller 290. FIG. 7 is a diagramillustrating an example of paper information according to the presentembodiment. As illustrated in FIG. 7, the printer controller 290 candiscriminate the paper information Q of the paper P by checking themeasured signal values S1′, S′2, and S′3 against the database that isinput in advance. As described above, the optical sensor 100 and theprinter controller 290 together serve as a paper-type discriminationdevice that discriminates the paper information Q using the reflectionlight of the paper P measured by the optical sensor 100.

The image forming operation that is performed by the image formingapparatus 200 according to the present embodiment is described. Firstly,the image data that is input from the host device 400 is transmitted bythe communication controller 280 to the printer controller 290 throughthe network or the like, and is stored in the ROM provided inside theprinter controller 290 as image data. The paper P is set to the opticalsensor 100 to determine the type of the paper P. Then, the paper P isset to the sheet tray of the sheet feeder 26. In so doing, the paperinformation Q indicating the type of the paper P is stored in theprinter controller 290. The paper information Q is checked against thedevelopment and transfer table 291 stored in the printer controller 290,and the optimal image-processing conditions that are in conformity withthe characteristics of the paper information Q are selected from thedevelopment and transfer table 291.

The sheet feeder 26 conveys the paper P set to the sheet tray to theregistration roller pair 256 using the feeding roller 254. When thesheet feeder 26 starts the sheet feeding operation as above, the imageforming unit 23 performs the latent-image writing operation, thedevelopment of a toner image, and the primary transfer from thephotoconductor 230 to the transfer belt 240 as described above, based onthe image-processing conditions and the image data stored in the printercontroller 290. After the primary transfer of the image onto thetransfer belt 240 is performed and the color toner image is developed,the registration roller pair 256 conveys the paper P at a prescribedtiming such that at the secondary transfer position N, the position ofthe toner image on the transfer belt 240 matches the position of thepaper P on which the image is to be formed. At the secondary transferposition N, the paper P is sandwiched between the transfer roller 242and the transfer belt 240 and the secondary transfer bias is appliedthereto. Accordingly, the secondary transfer of the toner image iscompleted. After the paper P passes through the fixing nip of the fixingdevice 25 and the toner image formed on the surface of the paper P isfixed by the application of heat and pressure, the paper P is ejected bythe output roller pair 258 to the paper output tray 270.

Next, a method of discriminating the paper-type information Q of thepaper P with the use of the optical sensor 100 according to the presentexample embodiment is described in detail.

In the initial state of the optical sensor 100, the pressing plane 103 aand the wall 131 are maintained in a state of contact. When the paper Pis inserted into the slot 111, the paper P is inserted between thepressing plane 103 a and the wall 131 along the inclined portion 103 b.When the paper P is inserted, the front side of the paper P abuts thewall 131, and the back side of the paper P abuts the pressing plane 103a, while the paper P pressing down the supporting member 103. Then, anedge of the paper P on the downstream side of the insertion directionabuts the abutment part 130.

In that state of abutment, cases in which a burr is formed on the edgeof the paper P that abuts the abutment part 130, as illustrated in FIG.4A and FIG. 4B, are described. When such a burr is present, asillustrated in FIG. 4B, a gap Δz may appear between the first aperture110 and the paper P when the paper P is simply abutted against the wall131 as in the related art. Note that the gap Δz is the misalignmentbetween the first aperture 110 and the paper P. It is considered thatwhen such a gap Δz appears, the position of the irradiation center Ovaries according to, for example, the degree of the burr, the differencein the paper quality of the paper P, and the degree of the resilience ofthe paper P. When the position of the irradiation center O varies, it isconsidered that the incidence angle varies and the intensity of each ofthe surface specular reflection light R1, the surface diffuse reflectionlight R2, and the internal diffusion reflection light R3 also varies.Moreover, it is considered that stray light entering through the gap Δzalso has an adverse effect on the measurement precision.

In order to avoid such situation, as described above, the optical sensor100 according to the present embodiment includes the first concaveportion 121 that is formed between the first aperture 110 and theabutment part 130 on the wall 131 side. Due to the provision of thefirst concave portion 121, as described above with reference to FIG. 4A,the burr of the edge of the paper P is accommodated in the first concaveportion 121. Accordingly, the gap Δz due to the burr of the edge of thepaper P is reduced or prevented, and the reflection light can preciselybe measured. In other words, the first concave portion 121 can preventthe object to be measured from being misaligned from the first aperture110.

The intensity of the output signals measured by the first photodetector15, and the second photodetector 13, and the third photodetector 17 whenthe paper P is in a state of abutment and irradiated with the lightemitted from the light source 11 are referred to as the measured signalvalues S′₁, S′₂, and S′₃, respectively. In the development and transfertable 291 stored in the printer controller 290, as illustrated in FIG.7, the intensities of the output signals that are measured in advanceare stored as reference signal values S₁, S₂, and S₃ together with thepaper-type information Q. More specifically, the reference signal valuesS₁, S₂, and S₃ and the paper-type information Q are stored as a databasein association with the image-processing conditions. The combinations ofthe reference signal values S₁, S₂, and S₃ may be stored as a paperdiscrimination database, which is independent of the development andtransfer table 291. Alternatively, the data may be stored in an externaldevice other than the printer controller 290, for example, in the hostdevice 400, and the data may be exchanged through the communicationenabled, for example, by the Internet.

The printer controller 290 compares the measured signal values S′₁, S′₂,and S′₃ with the reference signal values S₁, S₂, and S₃, respectively,to calculate a relevance ratio R as depicted in Formula 1 below.

$\begin{matrix}{R = {( {1 - {\frac{S_{1} - {S^{\prime}}_{1}}{S_{1} + {S^{\prime}}_{1}}}} ) \times ( {1 - {\frac{S_{2} - {S^{\prime}}_{2}}{S_{2} + {S^{\prime}}_{2}}}} ) \times ( {1 - {\frac{S_{3} - {S^{\prime}}_{3}}{S_{3} + {S^{\prime}}_{3}}}} )}} & \lbrack {{Formula}\mspace{14mu} 1} \rbrack\end{matrix}$

The printer controller 290 specifies the type of paper with the highestrelevance ratio R from the types of paper associated with the referencesignal values S₁, S₂, and S₃, and displays the specified type of paperas a result of paper discrimination. The printer controller 290 obtainsoptimal image-processing conditions for the result of paperdiscrimination from the development and transfer table 291, and controlsthe elements of the image forming apparatus 200 based on the obtainedoptimal image-processing conditions. Due to the configuration describedabove, the printer controller 290 serves as an adjuster that adjusts theimage-processing conditions of the image forming apparatus 200 accordingto the type of the paper P.

The optical sensor 100 includes the detector 133 that measures the lightreflected from the paper P, and the light source 11 that emits thelight. Note that the light is the S-polarized linear light. The detector133 includes the first photodetector 15 arranged on an optical path ofthe surface specular reflection light R1, and the second photodetector13 that is arranged in the optical path of the internal diffusionreflection light R3 on the XZ plane and detects the bundle of theP-polarized light that is orthogonal to the S-polarized light. Due tothis configuration described above, not only the surface specularreflection light R1 and the surface diffuse reflection light R2 but alsothe internal diffusion reflection light R3 including the densityinformation of the inside of the paper P or the like are measured.Accordingly, the types of the paper P including the surface conditionand the brand of the paper P can precisely be discriminated. Moreover,the detector 133 includes the third photodetector 17 that is arranged inthe optical path of the surface diffuse reflection light R2 outside theoptical path of the surface specular reflection light R1. Due to theconfiguration described above, the surface specular reflection light R1and the surface diffuse reflection light R2 can separately be measuredby calculating the difference between the output signal level of thefirst photodetector 15 and the output signal level of the thirdphotodetector 17. Accordingly, the reflection light can more preciselybe measured.

The optical sensor 100 includes supporting member 103 that appliespressure so as to press the paper P against the wall 131 when the paperP is in a state of abutment. Due to the configuration described above,the gap Δz between the first aperture 110 and the paper P can further bereduced, and the reflection light can precisely be measured.

The paper-thickness sensor 120 measures the displacement caused on thesupporting member 103 in the Z-axis direction to measure the thicknessof the paper P. The type of the object to be measured is discriminatedbased on the reflection light and the thickness measured by thepaper-thickness sensor 120. Due to the configuration described above,not only the light reflected from the paper P but also the thickness ofthe paper P are measured. Accordingly, the types of the paper P canfurther precisely be discriminated.

The optical sensor 100 includes the slot 111 into which the paper P isinserted in the X direction, i.e., the insertion direction, along thewall 131. Due to the configuration described above, the edge of thepaper P in the X direction abuts the abutment part 130, and thus thereflection light can easily be measured when the paper P is in a stateof abutment.

In the optical sensor 100 according to the present embodiment, the lightemitting elements provided for the light source 11 are vertical-cavitysurface-emitting laser (VCSEL) elements, and the light source 11 has aVCSEL array where a plurality of VCSEL elements are two-dimensionallyarranged. Due to the configuration described above, the laser beams canbe integrated with high density, and thus the light quantity increasesand the signal-to-noise ratio (S/N) can be improved. Accordingly, theprecision of the discrimination can be improved. Moreover, as thecontrast ratio of the speckle pattern of reflection light decreases byswitching on all the light-emitting points at the same time, theprecision of the discrimination can further be improved. As the laserbeams are integrated with high density, the laser beams concentratearound the optical axis of the collimator lens 12. Accordingly, thelaser beams can easily be collimated without depending on the quality ofthe collimator lens 12, and the incidence angle on the paper P can bemade uniform. Accordingly, the precision of the discrimination can beimproved.

Next, a second embodiment of the present invention is described. In thefollowing embodiments, only the features unique to each embodiment willbe described, and the description of the features in common with thefirst embodiment is omitted.

FIG. 8 is a diagram illustrating an example configuration of the opticalsensor 100 according to a second embodiment of the present invention. Insecond embodiment of the present invention, as illustrated in FIG. 8,the supporting member 103 of the optical sensor 100 includes a secondaperture 106.

The paper-thickness sensor 120 according to the second embodiment isarranged such that the cantilevered portion of the paper-thicknesssensor 120, which is the measuring part of the paper-thickness sensor120, penetrates the second aperture 106 and abuts the paper P. In otherwords, the paper-thickness sensor 120 abuts the portion of the paper Pexposed at the second aperture 106. Due to the configuration describedabove, the paper P can directly be measured without depending on theirregularities in the thickness of the components of the supportingmember 103. Accordingly, the thickness of the paper P can more preciselybe measured.

Next, a third embodiment of the present invention is described. FIG. 9is a diagram illustrating an example configuration of the optical sensor100 according to the third embodiment of the present invention. In thirdembodiment of the present invention, as illustrated in FIG. 9, thesupporting member 103 of the optical sensor 100 includes a secondconcave portion 122, in addition to the configuration of the secondembodiment described above. The second concave portion 122 may bereferred to as a second notch. In other words, the optical sensor 100has the second concave portion 122 that is formed so as to be opposed tothe first concave portion 121, on the other side of the paper P. Due tothe configuration described above, when a burr of the edge of the paperP remains in any of the upper and lower side of the Z direction, theedge of the paper P can be accommodated in one of the first concaveportion 121 and the second concave portion 122. Accordingly, the gap Δzis reduced, and the light reflected from the paper P can precisely bemeasured. Note that the second concave portion 122 may be a trench or ahole.

Next, a fourth embodiment of the present invention is described. FIG. 10is a diagram illustrating an example configuration of the optical sensor100 according to the fourth embodiment of the present invention. In thefourth embodiment, as illustrated in FIG. 10, the optical sensor 100includes an edge sensor 107 that is provided at an end portion of theslot 111 to detect that an edge of the paper P has passed while movingin the X direction. The edge sensor 107 is provided on a downstream sideof the first aperture 110 in the X direction, near the first concaveportion 121 in the X direction. The edge sensor 107 is, for example, areflective photointerrupter including a pair of light emitting elementsand light receiving elements, and detects whether or not the paper P haspassed under the edge sensor 107.

FIG. 11 is a block diagram depicting example processes performed by theoptical sensor 100 illustrated in FIG. 10. The measuring operation ofthe optical sensor 100 according to the fourth embodiment is describedwith reference to FIG. 11. In the initial state of the optical sensor100, in a similar manner to the first embodiment described above, thepressing plane 103 a and the wall 131 are maintained in a state ofcontact (S10). When the paper P is inserted through the slot 111, thepaper P moves forward in the X direction while pressing down thesupporting member 103 (S11).

When an edge of the paper P passes under the edge sensor 107, the lightemitted from the light emitting elements of the edge sensor 107 isreflected by the paper P and enters the light receiving elements of theedge sensor 107. Accordingly, the edge sensor 107 detects the paper Ppassing underneath (S12). The controller 105 uses the paper-thicknesssensor 120 to measure the thickness of the paper P when the edge sensor107 has detected the paper P passing underneath (S13). This measuringoperation is referred to as a paper-thickness measuring operation. Then,the controller 105 records the smallest value while the paper P ispassing as the thickness of the paper P (S14). After an edge of thepaper P reaches the abutment part 130 (S15), the paper P is pulled outin the −X direction. It is to be noted that the edge sensor 107 keepsdetecting the paper P passing underneath until the edge of the paper Phas been pulled out and passed under the edge sensor 107.

When the edge sensor 107 has detected the paper P passing underneath andthe edge of the paper P has been moved to a downstream side in the Xdirection of the edge sensor 107, the controller 105 controls the lightsource 11 to irradiate the paper P with light, and controls the detector133 to measure the light reflected from the paper P (S16). Thismeasuring operation is referred to as a reflection-light measuringoperation.

In the optical sensor 100, the paper P is securely inserted between thefirst aperture 110 and the supporting member 103 as described above, andthe thickness of the paper P can be measured in a condition that an edgeof the paper P is accommodated in the first concave portion 121.Accordingly, the thickness of the paper P can precisely be measured.Moreover, as the reflection-light measuring operation is performed whilethe paper P is inserted and pulled out as described above, thereflection light can be measured at a plurality of positions on thepaper P. In such cases, it is desired that the averages of therespective measured signal values S′₁, S′₂, and S′₃ be used for thepaper discrimination. When the averages of the measured signal valuesS′₁, S′₂, and S′₃ are used as described above, the distribution of thesurface condition or fiber density inside the paper P is balanced, andthe effect of variation can be reduced. Accordingly, the precision ofthe paper-type discrimination improves.

When the edge of the paper P further moves towards the −X direction, theedge sensor 107 detects that the paper P has been drawn out (S17). Whenit is detected that the paper P has been drawn out, the controller 105controls the light source 11 to cease irradiation, and terminatesmeasuring the reflected light (S18). Due to the configuration describedabove, the reflection light and the thickness of the paper P aremeasured only when the paper P is placed between the first aperture 110and the supporting member 103 with reliability. Accordingly, the powerconsumption can be reduced while the paper P is not inserted.

Note that the edge sensor 107 may be provided on an upstream side of thefirst concave portion 121, while the edge sensor 107 is on a downstreamside of the first aperture 110 in the X direction. In such cases, thedetector 133 starts measuring the reflection light after the edge sensor107 has detected the paper P passing and a prescribed length of timeaccording to the insertion speed of the paper P has passed. Moreover,the edge sensor 107 may be a contact-type sensor, and may detect thepaper P passing when an edge of the paper P touches the edge sensor 107.

In the following description, a fifth embodiment of the presentinvention is described with reference to FIG. 12. FIG. 12 is a diagramillustrating an example configuration of the optical sensor 100according to the fifth embodiment of the present invention. In the fifthembodiment, a third aperture 106 that serves as a light transmittingpart is formed at a position opposed to the first aperture 110 havingthe paper P therebetween, such that the center of the third aperture 106is on a straight line drawn from the irradiation center O parallel tothe Z-axis. Moreover, a transmission-light detector 18 that detects thelight quantity of the light that has passed through the third aperture106 is disposed below the center of the third aperture in the Z-axisdirection. The transmission-light detector 18 detects the internaldiffusion reflection light R3 that dispersed inside the paper P. Due tothe configuration described above, the transmission-light detector 18measures a measured signal value S′₄ that indicates the characteristicsof the paper P such as the thickness or fiber density of the paper P.The precision of the discrimination improves by using the measuredsignal value S′₄ described above together with the measured signalvalues S′₁, S′₂, and S′₃ for the paper-type discrimination of the paperP.

FIG. 13 is a diagram illustrating an example of the intensitydistribution of the transmission light measured by thetransmission-light detector 18 illustrated in FIG. 12. As illustrated inFIG. 13, it is known by experiment that the intensity distribution ofthe light that passes through the paper P has a peak in the reversedirection of the Z-axis under the irradiation center O. For this reason,in order to obtain a high signal-to-noise ratio (S/N), it is desiredthat the transmission-light detector 18 be disposed in the reversedirection of the Z-axis under the irradiation center O.

The present invention is not limited to the details of the exampleembodiments described above, and various modifications and improvementsare possible.

For example, the image forming apparatus 200 in the embodimentsdescribed above may be an optical plotter or a digital photocopier. Inthe above embodiments, cases in which the image forming apparatus 200 isprovided with four photoconductors were described. However, the imageforming apparatus 200 may be a monochrome image forming apparatus or aninkjet image forming apparatus. Although it is desired that the detector133 have a plurality of photodetectors, the detector 133 may be providedwith only one photodetector.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that within thescope of the appended claims, the disclosure of the present inventionmay be practiced otherwise than as specifically described herein. Forexample, elements and/or features of different illustrative embodimentsmay be combined with each other and/or substituted for each other withinthe scope of this disclosure and appended claims.

What is claimed is:
 1. An optical sensor comprising: an abutment partconfigured to abut one edge of an object to be measured; a wallextending along a side of the object to be measured and having a firstopening to pass light emitted to the object to be measured; and a firstconcave portion formed between the first opening and the abutment parton a side of the wall to position the object to be measured.
 2. Theoptical sensor according to claim 1, further comprising: a secondconcave portion formed between the first opening and the abutment partso as to face the first concave portion via the object to be measured.3. The optical sensor according to claim 1, further comprising: a lighttransmitting part formed on an opposite side of the first opening withreference to the object, the light transmitting part covering a part ofthe first opening or an entirety of the first opening; and atransmission-light detector configured to detect an amount of the lightthat has passed through the light transmitting part.
 4. The opticalsensor according to claim 1, further comprising: a light sourceconfigured to emit the light, the light being linearly polarized lighthaving a first polarization direction; and a detector configured tomeasure a reflection light of the light emitted to the object, thedetector including: a first photodetector disposed on an optical path ofthe light reflected from the object, and a second photodetector disposedon an optical path of bundle of lights reflected by diffuse reflectionfrom an incidence plane of the object and configured to detect thebundle of lights of a second polarization direction orthogonal to thefirst polarization direction.
 5. The optical sensor according to claim4, wherein the light source includes a light emitting element, and thelight emitting element is a vertical-cavity surface-emitting laserelements.
 6. The optical sensor according to claim 1, furthercomprising: a pressurizer configured to press the object against thewall.
 7. The optical sensor according to claim 1, wherein the object isinserted into a slit that extends along the wall in an insertiondirection parallel to the wall.
 8. The optical sensor according to claim7, further comprising: an edge sensor provided on a downstream side ofthe first opening in the insertion direction and on an upstream side ofthe first concave portion or near the first concave portion, andconfigured to detect that an edge of the object has passed while theobject is moving in the insertion direction.
 9. A paper-typediscrimination device comprising: the optical sensor according to claim1; and a controller configured to discriminate a paper type of theobject using the reflection light from the object measured by theoptical sensor.
 10. The paper-type discrimination device according toclaim 9, wherein the optical sensor includes a pressurizer configured topress the object against the wall, the paper-type discrimination deviceincludes a paper-thickness sensor configured to measure a thickness ofthe object based on a displacement caused to the pressurizer when thepressurizer presses the object against the wall, and the paper-typediscrimination device discriminates a type of the object using thereflection light and the thickness measured by the paper-thicknesssensor.
 11. The paper-type discrimination device according to claim 10,wherein the pressurizer has a second opening, and the paper-thicknesssensor includes a measuring part that abuts a portion of the objectexposed at the second opening.
 12. An image forming apparatuscomprising: the optical sensor according to claim
 1. 13. An imageforming apparatus comprising: the paper-type discrimination deviceaccording to claim
 9. 14. The image forming apparatus according to claim13, further comprising: an adjuster configured to adjust animage-forming condition of the image forming apparatus according to thepaper type of the object specified by the paper-type discriminationdevice.